JPS5893700A - Triaxial attitude control system of artificial satellite - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a three-axis attitude control system for an artificial satellite equipped with a flywheel having bias momentum.

Three mutually orthogonal axes fixed on the satellite, namely roll axis, pitch axis, and yaw axis, in order.

Satellites that are controlled to point in the direction of travel, perpendicular to the orbital plane, and toward the center of the Earth are called triaxial satellites.
An example of such a structure is shown in FIG. In the figure, (1) is a momentum wheel attached to the satellite so that its rotation axis is parallel to the pitch axis, (21 is an earth sensor that detects the satellite's roll and attitude angle around the pitch axis, (31 is a roll A roll/yaw offset thruster that generates a positive torque around the axis and a negative torque around the yaw axis, (4) a roll/yaw offset thruster that generates a negative torque around the roll axis and a positive torque around the yaw axis, (5)
) is the control electronic circuit, (6) is the roll axis, (7) is the pitch axis, and (8) is the yaw axis.

In an artificial satellite (hereinafter referred to as a bias momentum satellite) equipped with a flywheel having bias momentum (hereinafter referred to as a momentum wheel), by rotating the momentum wheel (1), angular momentum is imparted in the direction opposite to the pitch axis (71 direction). By generating a mutual conversion motion (roll/yaw conversion motion) in the orbit period of the roll angle and yaw angle and always controlling only the roll angle, it is possible to passively control the yaw angle as well.

For attitude control around the pitch axis, the earth sensor (2
) according to the pitch angle signal of the momentum wheel (1
) can be achieved relatively easily by increasing or decreasing the number of rotations, so it will not be discussed here.

The roll/yaw control of the bias momentum satellite configured in this example is based on the transfer function of the controlled object, Equation (1), which includes the dynamics of the star's roll and yaw angles and the characteristics of the earth sensor. Designed with

Here, Gpl(8) is the transfer function of the controlled object.

Input full roll/yaw offset thruster 131. +41
, and the output is the roll angle signal of the earth sensor +21. Ix and Iz are the moments of inertia of the entire satellite around the roll and yaw axes.

(2) is the orbital angular velocity, and hi+ is the angular momentum of the momentum wheel (-pitch axis direction is positive).

α is the offset angle of the roll/yaw offset thruster and is the Σ angle that determines the ratio of positive roll torque to negative yaw torque or negative roll torque to positive yaw torque. The ratio of roll torque to yaw torque when this thruster is injected is (cosα: -sinα
). Further, S is a Laplace operator.

It is well known that both the roll angle and yaw angle can be stably controlled by injecting and stopping the thruster having an appropriately set offset angle for the control target based on the roll angle signal of the earth sensor. .

However, for communication satellites and the like, it is required to improve the pointing accuracy of the antenna with respect to the ground station. To meet these requirements, the attitude control method described above uses an earth sensor as its attitude reference, and performs control such that the yaw axis of the satellite is directed toward the center of the earth, and the roll axis is aligned with the direction of travel of the artificial satellite. Because this is a method, even if the roll error, pitch error, and yaw error are completely controlled to zero, the degree of directivity may vary due to the influence of orbit errors, misalignment between the earth sensor and the antenna pointing axis, etc. descend.

Furthermore, it has the disadvantage that the directivity is reduced by 1 degree due to the influence of a yaw error with relatively low control accuracy.

This invention was made in order to improve the problems of the conventional method as described above. The present invention aims to provide a method for improving the pointing accuracy of an antenna with respect to a ground station by using an attitude angle detector that has an angle of 100 degrees.

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 2 is a block diagram showing an embodiment of the present invention. In this figure, 91 is an attitude angle detector that detects the roll angle and pitch angle with respect to the ground station.

The RF sensor (hereinafter referred to as RF') detects the roll angle and pitch angle from the received level of radio waves transmitted from the ground station.
sensor) is a typical example.

The roll/yaw control of the bias momentum satellite configured in this example is performed using the roll angle signal from the attitude angle detector (9), and this signal is the roll angle of the satellite when there is no orbit error or alignment error. Yaw angle, abbreviated as yaw angle (
There is a relationship that can be expressed by equation 21.

Here, Φ, θ, and V are the roll and pitch of the satellite, respectively.

Yaw angle, β1. β2 is a constant determined by the longitude of the satellite and the latitude and longitude of the ground station to which the RF sensor should point.

Therefore, when the roll/yaw control of the satellite is performed using the roll signal, the transfer function of the controlled object becomes as shown in Equation (31), assuming that β1 is sufficiently smaller than 1.

・Ga4 (8) t31 Here, Gp2 (S) is the transfer function of the controlled object when the input is the generated torque of the roll/yaw offset thruster and the output is ΦS, and G52 (8) is the transfer function of the attitude detector. be.

Also, it is assumed that Ix and It are equal, and are expressed in units.

Equation (31) is equivalent to Equation (11) in which the offset angle α of the thruster is replaced by α − βl.In other words, if the value obtained by subtracting βl from the offset angle of the thruster is considered as the equivalent offset angle, this system is Since it has exactly the same structure as the conventional system, it can be stably controlled using the same control method as the conventional system.In this case, in order to stabilize the system, α
- Since β1 is required to be positive, β1 is a positive amount when the satellite is stationary to the west of the ground station, and negative when it is stationary to the east, so in each case it increases and decreases the actual offset angle. By adding thrusters to the system, control can be achieved under exactly the same conditions as conventional systems. or,
Since the reference signal of Type 21 is the pointing error angle itself for the ground station, it is not affected by orbit errors or yaw control errors, achieving higher pointing accuracy than conventional methods. It goes without saying that it can be done.

As described above, according to the present invention, it is possible to improve the accuracy of pointing to a ground station, such as an antenna on a satellite, using the same control method as the conventional method, only by slightly modifying the offset angle of the thruster and attaching it.

[Brief explanation of drawings]

Figure 1 shows the conventional bias momentum! A configuration diagram of the parts related to three-axis attitude control of an artificial satellite. FIG. 2 is a block diagram showing an embodiment of the present invention.
11 is a momentum wheel, (2) is a satellite attitude angle detector, +31. +41 is the roll/yaw offset thruster, (5) is the control (l[l]11L child circuit, (6) is the roll axis. (η is the pitch axis, (8) is the yaw axis, (91 is the roll relative to the ground station, This is an attitude angle detector that detects the pitch angle. In addition, the same or corresponding parts in the two figures are indicated with the same reference numerals. Agent Shin Kuzuno - 111!! 1 Hi9 So Te Naka Yu 21st! l

Claims (1)

[Claims] A flywheel having a bias momentum and an attitude angle detector that detects a roll angle and a pitch angle with respect to a ground station direction as seen from a nine-artificial satellite. In a three-axis attitude control system for an artificial satellite that is equipped with two thrusters that generate torques of different polarities around in-plane axes including the roll axis and yaw axis of the artificial satellite, the output signal of the attitude angle detector is A three-axis attitude control system for an artificial satellite, characterized in that the thrusters are injected and stopped according to the following.